Heretofore, a clamp used in a supercharger has been manufactured as follows. Referring to FIGS. 1-3, there are shown a retainer (a) which is imperfectly circular in front elevation and can have a gutterlike cross section (FIG. 2), straps (b.sub.1) and (b.sub.2), a trunnion body (c), a trunnion cap (d), a T-shaped bolt, and a nut (f). Retainers as indicated by "a" are successively made by forming a band of stainless steel into a plurality of portions having a given shape with a multistage roll former and then trimming them to a given length. An unworked strap provided with a hole into which the T-shaped bolt (e) fits is blanked out from a band of stainless steel with a punching die, and then it is partially bent into a loop to make the strap (b.sub.1) or (b.sub.2) which is still flat except for the looped portion. The trunnion body (c) and the trunnion cap (d) are also made in a similar way. To be specific, an unworked member is blanked out from a sheet of stainless steel with a punching die, and then it is formed into a given shape with a press forming die to obtain the trunnion body (c) or trunnion cap (d). The trunnion cap (d) is press fitted into the trunnion body (d) by a press machine for assembly. The T-shaped bolt (d) is inserted into the looped portion of the strap (b.sub.1) so that the T-shaped head of the bolt is free to move, and other flat portions of the strap are secured together as by spot welding. The trunnion body (d) is inserted into the looped portion of the strap (b.sub.2) and anchored to this portion as by spot welding. The straps (b.sub.1) and (b.sub.2) into which the T-shaped bolt (e) and the trunnion body (c) are incorporated, respectively, are bent by a press machine so that they conform to the outer dimension and shape of the retainer (a), thus completing the preparation for the components.
The assembling operations are initiated by mounting the retainer (a) on a jig which can set the outer diameter of the retainer. Then, the strap (b.sub.1) incorporating the T-shaped bolt (e) is secured on one end of the retainer (a) and the strap (b.sub.2) incorporating the trunnion body (c) is secured on the outer end with jigs, and their respective pluarlity of locations are secured by spot welding. Then, these components are removed from the jigs and the threaded T-shaped bolt (e) is screwed into the trunnion body (c), and then the nut (f) which has been already prepared is screwed into the threaded portion of the bolt (e), thus completing the assemblying operations.
The aforementioned clamp for supercharger has problems: (i) It has a number of components requiring a large number of steps to manufacture and so the whole manufacturing process is complex; (ii) The conditions in which spot weldings are effected well are difficult to seek for, and the control of the components is required to be done sufficiently carefully; (iii) Spot weldings need special jigs, which together with the above respects (i) and (ii) increases the manufacturing cost of the clamp for supercharger. Further disadvantageously, small clamps whose diameters are less than 100 mm cannot be manufactured easily, because the multistage roll former is used to form the retainer (a).